Fix Django 2.0 incompatibility.

Description

Never too early to prepare for the future. Fixed based on this recommendation

django.utils.deprecation.RemovedInDjango20Warning: on_delete will be a required arg for
ForeignKey in Django 2.0. Set it to models.CASCADE on models and in existing migrations if you
want to maintain the current default behavior.
See https://docs.djangoproject.com/en/1.10/ref/models/fields/#django.db.models.ForeignKey.on_delete

This was causing open-craft/openedx-completion-aggregator#4 tests to fail once I added completion as a depenency, even on django 1.11. Probably some configuration was causing deprecation warnings to get promoted to errors. :woman_shrugging:

Review: @ciuin, @iloveagent57

Done

Assignee

Unassigned

Reporter

Open Source Pull Request Bot

Labels

None

Contributor Name

J. Cliff Dyer

Repo

edx/completion

Customer

None

Epic Link

None

OSCM Assignee

None

Platform Map Area (Levels 1 & 2)

None

Platform Map Area (Levels 3 & 4)

None

Blended Hour Utilization Percentage

None

edX Theme

None

edX Squad

None

Github Lines Added

7

Github Lines Deleted

4

Priority

Unset